FeatureName:
    | "current"
    | "entry"
    | "extends"
    | "false"
    | "fragment"
    | "grammar"
    | "hidden"
    | "import"
    | "infer"
    | "infers"
    | "interface"
    | "returns"
    | "terminal"
    | "true"
    | "type"
    | "with"
    | GrammarAST.PrimitiveType
    | string